NOAA Technical Memorandum NESS 71 NIMBUS-5 SOUNDER DATA PROCESSING SYSTEM PART II. RESULTS w. L. Smith H. M. Woolf C. M. Hayden W. C. Shen Washington, D.C. July 1975 UNITED STATES / NATIONAL OCEANIC AND / National Environmental DEPARTMENT OF COMMERCE ATMOSPHERIC ADMINISTRATION Satellite Service Rogers C. B. Morton, Secretary Robert M. White. Administrator David S. Johnson. Director This memorandum was originally prepared for the GARP Project Office, National Aero­ nautics and Space Administration, Goddard Space Flight Center, under Contract No. S-70249-AG. Mention of a commercial company or product does not constitute an endorsement by the NOAA National Environmental Satellite Service. Use for publicity or advertising purposes of information from this publication concerning proprietary products or the tests of such products is not authorized. ii CONTENTS Acknowledgments iv Abstract 1 1.0 Introduction 1 2.0 Measurement characteristics of the Nimbus-5 sounders 2 2.1 The ITPR experiment 3 2.2 The NEMS experiment 6 2.3 The SCR experiment 7 3.0 Characteristics of the amalgamated Nimbus-5 sounding data 8 4.0 An intercomparison of the meteorological parameters derived from Nimbus-5 and those from radiosonde and NOAA-2 VTPR vertical temperature cross sections . 10 5.0 An intercomparison of results obtained with the Nimbus-5 retrieval algorithm vs. real-time regression ..... 14 6.0 Application of the Nimbus-5 sounding data to the study of tropical circulation . • . 16 Application of the Nimbus-5 sounding system to Southern Hemisphere data . 21 8.0 An intercomparison of radiosonde and Nimbus-5-derived cross­ sections during the M4TEX . 24 9.0 Evaluation of the Nimbus-5 sounding system during the May (1974) GARP Data Systems Test (DST) 28 10.0 Future developments 33 References . iii ACKNOWLEDGMENTS The processing system described in this report was developed with the close cooperation oftheNEMS and SCR experimenters. We wish to express our appreciation to Drs. D. Staelin and J. T. Houghton and their colleagues at the M.I.T. and Oxford Universities, respectively, for their continual support during the development of the Nimbus-5 data processing system. The assistance provided by the Meteorological Data Handling Center and the Technical Control Center of the Nimbus project is also greatly appreciated. Messrs. P. Gary, W. Holmes, and K. Iobst were responsible for converting the NESS-developed C.D.C. computer software required to implement the algorithms (described in part I of this report) to run on the NASA GISS IBM 360 for D.S.T. application. Finally, but most impor­ tant, we thank all the members of the Radiation Branch, MSL and Computation Group of NESS Office of Research for their contributions to the develop­ ment, debugging, and analysis of the results of this processing system. In particular we thank Messrs. H. Howell, P. G. Abel, N. Grody, M. C. Chalfant, L. Mannello, P. Pellegrino, R. Ryan, F. Nagle, G. Callan, W. Jacob and C. Jacobson for their invaluable assistance in these aspects of the system development. Out thanks also go to Mrs. M. Schwier for typing this technical manuscript. iv ... - NIMBUS-5 SOUNDER DATA PROCESSING SYSTEM PART II: Results W. L. Smith, H. M. Woolf, C. M. Hayden, W. C. Shen National Environmental Satellite Service National Oceanic and Atmospheric Administration Washington, D. C. ABSTRACT. The Nimbus-5 spacecraft carries infrared and microwave radiometers for sensing the temperature distribution of the atmosphere. Methods have been developed for obtaining temperature profiles from the combined set of infrared and microwave radiation measurements. Part I of this report described the algorithms used to determine (a) vertical tempera­ ture and water vapor profiles, (b) cloud height, fractional coverage, and liquid water content, (c) surface temperature, and (d) total outgoing longwave radiation flux. This second part of the report presents the various meteorological results obtained from the application of the Nimbus-5 sounding data processing system during 1973 and 1974. 1.0 INTRODUCTION The Nimbus-5 spacecraft (launched December 11, 1972) carries several radiometers for sensing the temperature, water vapor, and cloud distribu­ tion of the atmosphere. The Infrared Temperature Profile Radiometer (ITPR), a second generation scanning infrared radiometer, observes the temperature distribution of the earth's surface, the troposphere and lower stratosphere with a spatial resolution of 15 n.mi. The Selective Chopper Radiometer (SCR), developed in the .United Kingdom, enables temperature profiles to be obtained up to the stratopause. The Nimbus-E Microwave Spectrometer (NEMS), observes.the vertical temperature-distri~ bution through and below clouds. Since the infrared and microwave radiometers on Nimbus-5 provide highly complementary observations, one would expect to obtain better temperature profile results using the combined set of infrared and microwave observations than with either set individually. The National Environmental Satellite Service (NESS), with the financial support 2 of the Rational ~eronautics and ~pace ~dministration (NASA) and with the technical cooperation of the NEMS and SCR experimenters at the Mass­ achusettes Institute of Technology and Oxford University, respectively, has developed algorithms for obtaining temperature profiles on a global basis using infrared and microwave radiances individually and in combination as described in Part I of this report (Smith, et al., 1974). This data processing system was developed to provide global meteorological data sets to support the Global Atmospheric Research Program (GARP) and other research programs. The essential charac­ toeristics of this data processing system are reviewed and some of the significant meteorological results obtained during 1973 and 1974 are presented in this report. 2.0 MEASUREMENT CHARACTERISTICS OF THE NIMBUS-5 SOUNDERS Figure 1 shows the ITPR, NEMS and SCR instruments aboard the Nimbus-5 spacecraft. The ITPR (Smith, et al., 1972) measures radiation in seven different spectral intervals. Two of the spectral intervals are in the window regions at 3.7 vm and 11 vm for the purpose of detecting clouds and for obtaining surface temperatures, even when a partial cloud cover exists in the instrument's field-of-view. There are four atmospheric temperature profiling channels in the 15-vm band and a single water co 2 vapor channel at 20 vm in the rotational water vapor absorption band. The instrument has a linear spatial resolution of 15 n.mi. and spatially scans in Order to circumvent clouds and to obtain uniform earth coverage. The NEMS instrument (Staelin; et al., 1972) is composed of five channels, three of which are in the neighborhood of the 0.5-cm oxygen absorption band and whose measurements are therefore useful for ob­ taining atmospheric temperature profiles. The instrument has relatively low spatial resolution (100 n.mi.) and does not spatially scan. However, these limitations are offset by its most important characteristic: the radiances it senses are not attenuated significantly by clouds. Thus, this instrument's measurements will yield temperature profiles through and below clouds. Also because it is possible to achieve much higher spectral resolution at microwave frequencies, the weighting functions are relatively sharp. This characteristic is particularly helpful in resolving the tropospause region. The SCR (Hought9n and Smith, 1972) is composed of sixteen channels. Four of its channels are in the most strongly absorbing portion of the 15-vm co band and employ co2 gas cells to separate absorption line center emissLons2 from contributions from the line wings. When combined, they provide unique measurements, with relatively narrow weighting functions, of the temperature of the middle and upper stratosphere. 3 Figure 2 illustrates the vertical weighting functions for various spectral channels of the Selective Chopper Radiometer (SCR), Infrared Temperature Profile Radiometer (ITPR), and the Nimbus-E Microwave §Pectrometer-(NEMS) instruments flown aboard the Nimbus-5 satellite. The weighting function curves depict the layers most vividly sensed by the particular spectral channels. The SCR weighting functions pertain to high spectral resolution measurements of radiation due to the strong absorption lines at the center of the 15-~m COz band. The ITPR weighting functions are due to four spectral intervals of the 15-~m C02 band ranging from the center to the wing of the band. The NEMS weighting functions are due to a complex of oxygen absorption lines near 0.5 em. Differences in the weighting function widths and peak values are due to differences in the effective spectral resolutions of the various instruments~ The earth fields of view for the ITPR, NEMS, and SCR are shown in figure 3. As shown, the ITPR cluster samples within three different grids, one to the right of the orbital track, one in the center, and one to the left. NEMS and SCR samples only along the orbital track. The instantaneous resolutions of the ITPR, NEMS and SCR are 35 km, 192 km, and 43 km, respectively. 2.1 The ITPR Experiment For useful temperature profile determinations from infrared radiation data, it is necessary to detect the existence of any cloud contributions to the observed radiances and to correct for,these contri­ butions before attempting to calculate the atmospheric temperature profile. For this purpose, the ITPR experiment employs moderate spatial resolution (15 n.mi.), spatial scanning, and channels for obtaining simultaneous radiance observations in the 3.7-~m and 11-~m windows. Since clouds im­ pose the major obstacle to sounding using infrared measurements, it is wortowhile to explain how the ITPR experiment attempts to alleviate this deficiency. Since molecular absorption is small in the 3.7-~m and 11-~m window regions, these ITPR window channels sense only the radiation from the earth's surface and any clouds within the instrument's field of view. When sensing a uniform and opaque scene (e.g., the earth's surface) they observe the same brightness temperature. However, when sensing a non­ uniform or non-opaque scene (e.g., broken clouds within the instrument's field of view) they observe different brightness temperatures.